There are 8 US Post Offices in Mcpherson County serving a total of 25,492 residents equating to 3,187 residents per post office. It's estimated that approximately 40,688 packages are handled across the 8 county post offices annually. McPherson County (standard abbreviation: MP) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 29,180. The largest city and county seat is McPherson. The county is named for Civil War General James B. McPherson."